Movement of Materials Movement of Materials Across MembranesAcross Membranes

Background InformationBackground Information

Most cells exist in liquid, making it easy for Most cells exist in liquid, making it easy for materials to move into and out of the cell.materials to move into and out of the cell.Every cell membrane is Every cell membrane is selectively selectively permeablepermeable, meaning that some , meaning that some substances but not others can cross them.substances but not others can cross them.Particles have a tendency to move from a Particles have a tendency to move from a region where they are more numerous to a region where they are more numerous to a region where they are less numerous.region where they are less numerous.

A Concentration Gradient is…A Concentration Gradient is…

……a difference in the number of a difference in the number of molecules of a substance in two molecules of a substance in two neighboring regions.neighboring regions.

Molecules tend to move Molecules tend to move downdown their their concentration gradients (higher to lower concentration gradients (higher to lower concentration).concentration).

Particles of a substance tend to go Particles of a substance tend to go from areas of higher concentration to from areas of higher concentration to areas of lower concentration.areas of lower concentration.

A.A. TrueTrue

B.B. FalseFalse

It's not simply a case of movement in one direction. Particles move in both directions, but because one side has more particles to start with, they are more likely to move in one direction than the other. When both sides have the same number of particles, they are just as likely to move one way as the other way, so there will be no change in amounts - both sides will stay equal.

Diffusion is…Diffusion is…

……the process by which molecules of the process by which molecules of a substance move from areas of a substance move from areas of higher concentration to areas of lower higher concentration to areas of lower concentration.concentration.

……the driving force behind the the driving force behind the movement of materials across the movement of materials across the plasma membrane.plasma membrane.

A.A. A barrier separates two different substances.A barrier separates two different substances.B.B. The barrier is removed, and the substances move down The barrier is removed, and the substances move down

their concentration gradients.their concentration gradients.C.C. Equilibrium is reached.Equilibrium is reached.

Osmosis is…Osmosis is…

……the diffusion of water the diffusion of water molecules through a molecules through a selectively permeable selectively permeable membrane from an membrane from an area of greater area of greater concentration of water concentration of water to an area of lesser to an area of lesser concentration of water.concentration of water.

Based on the concept of osmosis, what Based on the concept of osmosis, what would you expect to happen in this setup?would you expect to happen in this setup?

A.A. No movement of water will occur.No movement of water will occur.

B.B. Water will move in both directions equally.Water will move in both directions equally.

C.C. The net movement of water will be from The net movement of water will be from side B to side A.side B to side A.

D.D. The net movement of water will be from The net movement of water will be from side A to side B.side A to side B.

Osmosis TerminologyOsmosis TerminologyWhen comparing two solutions…When comparing two solutions…

……solutions with higher concentrations of solutions with higher concentrations of solute are solute are hypertonichypertonic((hyperhyper means "above"). means "above").

……solutions with lower concentrations of solutions with lower concentrations of solute are solute are hypotonichypotonic((hypohypo means “below”). means “below”).

……solutions in which the concentrations are solutions in which the concentrations are equal are equal are isotonicisotonic((isosisos means “equal”). means “equal”).

Which of the following correctly Which of the following correctly labels this setup?labels this setup?

A.A. left: isotonic / right: isotonicleft: isotonic / right: isotonic

B.B. left: isotonic / right: hypertonicleft: isotonic / right: hypertonic

C.C. left: hypertonic / right: hypotonicleft: hypertonic / right: hypotonic

D.D. left: hypotonic / right: hypertonicleft: hypotonic / right: hypertonic

Imagine that the membrane shown Imagine that the membrane shown below is impermeable to the solute below is impermeable to the solute molecules but permeable to water. molecules but permeable to water.

Which way will water flow?Which way will water flow?

A.A. left to rightleft to right

B.B. right to leftright to left

Normally, in the process of osmosis, the Normally, in the process of osmosis, the net flow of water molecules into or out of net flow of water molecules into or out of the cell depends upon differences in thethe cell depends upon differences in the

A.A. rate of movement of molecules inside rate of movement of molecules inside the cellthe cell

B.B. concentration of water molecules inside concentration of water molecules inside and outside the celland outside the cell

C.C. rate of molecular motion on either side rate of molecular motion on either side of the cell membraneof the cell membrane

D.D. concentration of enzymes on either side concentration of enzymes on either side of the cell membrane of the cell membrane

Facilitated Diffusion Facilitated Diffusion

Diffusion of a substance Diffusion of a substance through a transport through a transport protein embedded in a protein embedded in a membrane.membrane.

In facilitated diffusion, In facilitated diffusion, solute particles pass solute particles pass through a channel in a through a channel in a transport protein.transport protein.

Passive TransportPassive TransportDiffusion, osmosis, and Diffusion, osmosis, and facilitated diffusion are all facilitated diffusion are all forms of passive transport forms of passive transport across the plasma across the plasma membrane because membrane because energy is not required for energy is not required for them to happen.them to happen.Like riding a bike down a Like riding a bike down a hill, no energy is needed.hill, no energy is needed.

Facilitated Diffusion

Outside Cell

Inside Cell

TransportProtein

Higher Concentration of Molecules

Lower Concentration of Molecules

Active TransportActive Transport……involves a substance being involves a substance being forced through a transport forced through a transport protein in the plasma protein in the plasma membrane against the membrane against the concentration gradient (from concentration gradient (from lower to higher lower to higher concentration).concentration).

Like riding a bike up a hill, an Like riding a bike up a hill, an energy boost is required.energy boost is required.

Active Transport

Outside Cell

Inside Cell

TransportProtein

Higher Concentration of Molecules

ENERGYLower Concentration

of Molecules

Molecule to be

carried

Active Transport

Outside Cell

Inside Cell

Molecule is transported to the other side of the membrane

Which of the following types of transport Which of the following types of transport across membranes was compared to across membranes was compared to riding a bike up a hill?riding a bike up a hill?

A.A. diffusiondiffusion

B.B. osmosisosmosis

C.C. active transportactive transport

D.D. facilitated diffusionfacilitated diffusionLike an enzyme, a transport protein recognizes a specific solute, molecule or ion. During active transport, the protein uses energy, usually moving the solute in a direction from lesser concentration to greater concentration.

Endocytosis and ExocytosisEndocytosis and Exocytosis

……the processes of the processes of taking material into taking material into (endocytosis) or out (endocytosis) or out of (exocytosis) the of (exocytosis) the cell by means of cell by means of pockets of the cell pockets of the cell membrane.membrane.

Exocytosis & Exocytosis & EndocytosisEndocytosis

What process is shown here?What process is shown here?

A.A. osmosisosmosis

B.B. exocytosisexocytosis

C.C. endocytosisendocytosis

D.D. facilitated diffusionfacilitated diffusion